1. Field of the Invention
This invention relates to a method for desensitization using a desensitizing composition and, more specifically, to a method using a desensitizing composition which reduces or eliminates the effect of a developer (an electron accepting compound, e.g., a solid acid) capable of coloring a color former (a substantially colorless, electron donating organic compound).
2. Description of the Prior Art
It has long been known to form a color image through the reaction of a color former and a color developer. The principle is practically utilized in pressure sensitive copying sheets (as disclosed, for example, in U.S. Pat. Nos. 2,505,470, 2,505,489, 2,550,471, 2,548,366, 2,712,507, 2,730,456, 2,730,457 and 3,418,250) and heat sensitive recording sheets (as disclosed, for example, in Japanese Patent Publication No. 4160/68 and U.S. Pat. No. 2,939,009). Furthermore, a printing method has also been known in which a color image is formed by supplying an ink containing a color former through a medium such as a stencil to a sheet coated with a color developer (as disclosed in German Pat. No. 1,939,962).
Pressure copying sheets can be prepared by dissolving a color former in a solvent such as a chlorinated paraffin, an alkylnaphthalene, an alkylated diphenylethane or an alkylated diphenylmethane, dispersing the color former solution in a binder or microencapsulating the color former solution, and then coating the composition on a support such as a paper or a synthetic resin film, on the one hand, and coating, as a color developer, an acid clay, a phenol-formaldehyde resin, a metal salt of an aromatic carboxylic acid or the like, on the other hand.
Heat sensitive recording sheets can be prepared by coating, on a support, a color former and a color developer together with a heat-fusible substance such as acetanilide. Heat-fusible substances are those substances which melt by heating and dissolve the color former.
In general, a color former and a color developer are coated respectively over the entire surface of a support. Therefore, it is necessary to prevent a color reaction in some way in the portions in which the formation of a color image is not required or permitted. For this purpose, a desensitizing agent is usually coated by printing on certain portions of a color developer coated layer to prevent the color reaction. Known desensitizing agents, for example, include long chain primary alkylamines such as dodecylamine and quaternary ammonium salts such as dodecyltrimethyl-ammonium chloride as described in U.S. Pat. No. 2,777,780; monoalkylamines, alkylamines or tertiary amines comprising ethanolamine adducts with ethylene oxide as described in Japanese Patent Publication No. 29546/71; secondary alkylamines such as didodecylamine, tertiary alkylamines such as triethylamine, primary arylamines such as aniline or aralkylamines such as benzylamine.
However, conventional desensitizing agents have disadvantages and it is, therefore, desired to develop superior desensitizing agents.
Disadvantages of the conventional desensitizing agents are set forth below.
1. Insufficient desensitizing effects are exhibited by conventional desensitizing agents and, in particular, no effects are exhibited for xanthene color formers such as 7-diethylamino-3-dibenzylaminofluoran.
2. Conventional desensitizing agents have an unpleasant amine odor and the surface on which they are coated is colored.
3. The images formed, due to the color reaction, on the surface on which conventional desensitizing agent are coated undergo a marked discoloration and fading.
4. When conventional desensitizing agents are left together with microcapsules, swelling of the membranes of the microcapsules results, and as the case may be, the membranes can even be destroyed.